The proposed project is an investigation of some of the factors which may regulate the development of retinofugal projections in vertebrates. We have demonstrated that pigment in the embryonic optic stalk may be exerting some inhibitory influence on the growth of retinal axons in the ferret. We are currently examining albino and pigmented rat embryos with anatomical methods which permit us to see if the position of growing axons in the stalk determines if these axons will cross or remain uncrossed at the optic chiasm. We also propose to examine the neurochemical development of the embryonic chick optic tectum. We are examining the high affinity amino acid uptake systems developing tectal cells to determine if these factors have any chemotactic influence on ingrowing retinal axons.